Liquid crystal display (LCD) devices using liquid crystal compositions are widely utilized for display of clocks, calculators, and word processors, etc. These LCD devices utilize the optical anisotropy and dielectric anisotropy of liquid crystal compounds. Operation modes of LCD devices mainly include phase change (PC), twisted nematic (TN), super twisted nematic (STN), bistable twisted nematic (BTN), electrically controlled birefringence (ECB), optically compensated bend (OCB), in-plane switching (IPS), and vertical alignment (VA), etc., which use one or more polarizing plates for display. Further, many studies have recently been made on a mode that exhibits electric birefringence by applying an electric field to an optically isotropic liquid crystal phase (Patent Documents 1 to 14 and Non-patent Documents 1 to 3).
Moreover, wavelength tunable filters, wavefront control devices, liquid crystal lenses, aberrational correction devices, aperture control devices, optical head devices and so on that utilize the electric birefringence of a blue phase as one of the optically isotropic liquid crystal phases have been proposed (Patent Documents 10 to 12).
According to the driving mode, LCD devices are classified into passive matrix (PM) and active matrix (AM) types. PM type is classified into static type and multiplex type, etc. AM type is classified into thin film transistor (TFT) type and metal insulator metal (MIM) type, etc.
These LCD devices each contain a liquid crystal composition with suitable physical properties. To improve characteristics of an LCD device, the liquid crystal composition preferably has suitable physical properties. General physical properties necessary for a liquid crystal compound as a component of a liquid crystal composition include:    1) chemical and physical stability,    2) a high clearing point (liquid crystal phase-isotropic phase transition temperature),    3) a low minimum temperature of the liquid crystal phase (a nematic phase, a cholesteric phase, a smectic phase, and an optically isotropic liquid crystal phases like a blue phase, etc.),    4) good compatibility with other liquid crystal compounds,    5) an appropriately large dielectric anisotropy, and    6) an appropriately large optical anisotropy.
Particularly, in view of lowering the driving voltage, a liquid crystal compound having both a large dielectric anisotropy and a large optical anisotropy is preferred for the optically isotropic liquid crystal phase.
When a liquid crystal composition including a liquid crystal compound with chemical and physical stability (the 1st physical property) is used in an LCD device, the voltage holding ratio can be increased.
In addition, a liquid crystal composition including a liquid crystal compound having a high clearing point or a low minimum temperature of liquid crystal phase (the 2nd and 3rd physical properties) can have a larger temperature range of nematic phase or optically isotropic liquid crystal phase, and can be used in display devices in a broad temperature range. To exhibit physical properties that are hardly exhibited by a single compound, a liquid crystal compound is usually mixed with a large number of other liquid crystal compounds to prepare a liquid crystal composition for use. Hence, a liquid crystal compound used in an LCD device preferably has good compatibility with other liquid crystal compounds (the 4th physical property). Recently, LCD devices superior in display performance such as contrast, display capacity, response time and so on are particularly required. Regarding the used liquid crystal material, a liquid crystal composition with a low driving voltage is required. Also, in order to drive, at a low voltage, an optical device that is driven in an optically isotropic liquid crystal phase, it is preferred to use a liquid crystal compound with large dielectric anisotropy and optical anisotropy.